The present invention relates to a power supply circuit, a display driver, an electro-optical device, an electronic instrument, and a method of controlling a power supply circuit.
As a liquid crystal display (LCD) panel (display panel in a broad sense) used in an electronic instrument such as a portable telephone, a simple matrix type LCD panel and an active matrix type LCD panel using a switch element such as a thin film transistor (hereinafter abbreviated as “TFT”) have been known.
The simple matrix type LCD panel easily reduces power consumption in comparison with the active matrix type LCD panel. However, it is difficult to increase the number of colors and display a video in the simple matrix type LCD panel. The active matrix type LCD panel is suitable for increasing the number of colors and displaying a video. However, it is difficult to reduce power consumption of the active matrix type LCD panel.
In recent years, an increase in the number of colors and display of a video have been increasingly demanded for a portable electronic instrument such as a portable telephone in order to display a high-quality image. Therefore, the active matrix type LCD panel has been widely used instead of the simple matrix type LCD panel.
The simple matrix type LCD panel or the active matrix type LCD panel is driven so that the voltage applied to a liquid crystal forming a pixel is alternately changed. As such an alternating drive method, a line inversion drive and a field inversion drive (frame inversion drive) have been known. In the line inversion drive, the polarity of the voltage applied to the liquid crystal is reversed in units of one or more scan lines. In the field inversion drive, the polarity of the voltage applied to the liquid crystal is reversed in field (frame) units.
The voltage level applied to a pixel electrode forming a pixel can be decreased by changing a common electrode voltage (common voltage) supplied to a common electrode opposite to the pixel electrode corresponding to inversion drive timing.
The inversion drive increases power consumption since an electric charge is repeatedly charged and discharged. JP-A-2004-184840 discloses a technology of reducing power consumption by reutilizing an electric charge discharged from a data line of the LCD panel.
However, the load of the common electrode of the LCD panel is almost constant, and the power supply capability of a power supply circuit which supplies the common electrode voltage is determined taking into consideration the maximum value of the amount of electric charge to be charged and discharged. Therefore, unnecessary power consumption occurs when the power supply capability is not required.
In recent years, an increase in resolution and grayscale of the LCD panel has been demanded. Therefore, an accurate and high drive capability is required so that current consumption is increased. Therefore, the image quality of the LCD panel is affected by only a small change in voltage level or the like, whereby a horizontal crosstalk problem or the like occurs.
Along with an increase in grayscale of the LCD panel, grayscale characteristics vary depending on the LCD panel, so that a complicated process is required to display a desired image. Therefore, it is important to display a desired image corresponding to various grayscale characteristics.